Chlorophyll a & b: The Hidden Drivers of Plant Light Absorption
When we talk about plant lighting, we often mention PAR (Photosynthetically Active Radiation). But what determines which wavelengths are actually useful to plants?
The answer lies in two critical pigments: Chlorophyll a and Chlorophyll b.
What Is Chlorophyll?
Chlorophyll is the pigment responsible for absorbing light in photosynthesis. While plants contain various pigments, Chlorophyll a and Chlorophyll b are the most important for capturing light energy.
Chlorophyll a Absorption Peaks
Chlorophyll a is the primary pigment found in all photosynthetic organisms. It has two strong absorption peaks:
- Around 430 nm (blue light)
- Around 662 nm (red light)
These wavelengths provide the energy needed to drive the main chemical reactions in photosynthesis.
Chlorophyll b Absorption Peaks
Chlorophyll b plays a supporting role, broadening the range of light plants can use. Its absorption peaks are:
- Around 453 nm (blue light)
- Around 642 nm (red-orange light)
By absorbing different wavelengths than chlorophyll a, chlorophyll b helps capture more light energy, especially in shaded or indirect light conditions.
Why This Matters for Grow Lights
Understanding the absorption spectrum of chlorophyll helps growers choose or design lighting that truly supports plant health. Lights with strong emission in the 430–460 nm and 640–670 nm ranges will be more effective for photosynthesis, especially for indoor and greenhouse plants.
Summary
| Pigment | Main Absorption Peaks | Role in Photosynthesis |
|---|---|---|
| Chlorophyll a | 430 nm & 662 nm | Primary light absorber and reaction driver |
| Chlorophyll b | 453 nm & 642 nm | Accessory pigment, broadens light use |
Together, these pigments explain why PAR is defined as 400–700 nm, and why blue and red LEDs are so commonly used in horticulture.
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